Krieger was born to a family of German origins, in the small city of Cerro Largo, in the southernmost state of Brazil, Rio Grande do Sul.
There, while he was a student, he began working with Prof. Rubens Maciel at the Cardiology Department and decided to pursue a university career in the clinical area.
Since Brazil had few physiological research labs at the time, the program was partly supervised by Argentine physiologists, under Prof. Bernardo Houssay's leadership (Nobel Prize, 1947).
His sponsor was Prof. Miguel Rolando Covian, the new departmental chairman and an Argentine neurophysiologist who had belonged to Prof. Houssay's group and who became very impressed with Krieger during his formative years in Porto Alegre and Buenos Aires.
As a result, new laboratories headed by Krieger's former pupils were created in several other universities, in Ribeirão Preto, São Paulo, Belo Horizonte, Vitória, Porto Alegre and Recife.
He was also a pioneer in using the rat as a model for the study of blood pressure regulation in sleep and exercise, as well as in the neural recording of electrical activity of the sympathetic system in physiological conditions.